Wheel skirt shielding upper tire sidewall

ABSTRACT

An upper wheel skirt assembly for increasing the propulsive efficiency of a wheeled vehicle having rearward wheels otherwise exposed to headwinds comprising a wheel skirt panel assembly mounted laterally adjacent to a wheel assembly and disposed to shield upper sidewalls of the wheel assembly from headwinds otherwise impinging thereon.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of patent application Ser.No. 15/430,037, filed Feb. 10, 2017 by Garth L. Magee.

BACKGROUND Field

The present embodiment relates to an apparatus for the reduction ofaerodynamic drag on vehicles having wind-exposed wheels of a wheelassembly mounted underneath the vehicle body, such as on largecommercial trucks.

Description of Prior Art

Inherently characteristic of rotating vehicle wheels, and particularlyof spoked wheels, aerodynamic resistance, or parasitic drag, is anunwanted source of energy loss in propelling a vehicle. Parasitic dragon a wheel includes viscous drag components of form (or pressure) dragand frictional drag. Form drag on a wheel generally arises from thecircular profile of a wheel moving though air at the velocity of thevehicle. The displacement of air around a moving object creates adifference in pressure between the forward and trailing surfaces,resulting in a drag force that is highly dependent on the relative windspeed acting thereon. Streamlining the wheel surfaces can reduce thepressure differential, reducing form drag.

Frictional drag forces also depend on the speed of wind impingingexposed surfaces, and arise from the contact of air moving oversurfaces. Both of these types of drag forces arise generally inproportion to the square of the relative wind speed, per the dragequation. Streamlined design profiles are generally employed to reduceboth of these components of drag force.

The unique geometry of a wheel used on a vehicle includes motion both intranslation and in rotation; the entire circular outline of the wheeltranslates at the vehicle speed, and the wheel rotates about the axle ata rate consistent with the vehicle speed. Form drag forces arising fromthe moving outline are apparent, as the translational motion of thewheel rim must displace air immediately in front of the wheel (andreplace air immediately behind it). These form drag forces arisingacross the entire vertical profile of the wheel are therefore generallyrelated to the velocity of the vehicle.

As the forward profile of a wheel facing the direction of vehicle motionis generally symmetric in shape, and as the circular outline of a wheelrim moves forward at the speed of the vehicle, these form drag forcesare often considered uniformly distributed across the entire forwardfacing profile of a moving wheel (although streamlined cycle rims canaffect this distribution somewhat). This uniform distribution ofpressure force is generally considered centered on the forward verticalwheel profile, and thereby in direct opposition to the propulsive forceapplied at the axle, as illustrated in FIG. 17.

However, as will be shown, frictional drag forces are not uniformlydistributed with elevation on the wheel, as they are not uniformlyrelated to the speed of the moving outline of the wheel rim. Instead,frictional drag forces on the wheel surfaces are highly variable anddepend on their elevation above the ground. Frictional drag must beconsidered separate from form drag forces, and can be more significantsources of overall drag on the wheel and, as will be shown, thereby onthe vehicle.

Vehicles having wind-exposed wheels are particularly sensitive toexternal headwinds reducing propulsive efficiency. Drag force on exposedwheels increases more rapidly on upper wheel surfaces than on vehicleframe surfaces, causing a non-linear relation from rising wind speedsbetween net drag forces on vehicle frame surfaces versus net drag forceson vehicle wheel surfaces.

Since upper wheel surfaces are moving against the wind at more than thevehicle speed, the upper wheel drag forces contribute more and more ofthe total vehicle drag as external headwinds rise. Thus, as externalheadwinds rise, a greater fraction of the net vehicle drag is shiftedfrom vehicle frame surfaces to upper wheel surfaces.

Moreover, upper wheel drag forces must be overcome by a propulsivecounterforce applied at the axle. Such propulsive counterforces suffer amechanical disadvantage against the upper wheel drag forces, since eachnet force is applied about the same pivot point located at the bottomwhere the wheel is in stationary contact with the ground. Thismechanical advantage that upper wheel drag forces have over propulsivecounterforces further augments the effective vehicle drag that exposedupper wheels contribute under rising headwinds. As a result of thesemagnified effects of upper wheel drag on resisting vehicle propulsion,vehicle drag is more effectively reduced by reducing the aerodynamicpressure on the upper wheel surfaces while leaving the lower wheelsurfaces exposed to impinging headwinds.

Furthermore, shielding the lower wheel surfaces can cause a net increasein vehicle drag, and a loss in propulsive efficiency. Not only does thepropulsive counterforce applied at the axle have a mechanical advantageover the lower wheel drag forces, but shielding the lower wheel surfacesusing a deflector attached to the vehicle body shifts the drag forcefrom being applied at the lower wheel to an effective higher elevationat the axle, thereby negating any mechanical advantage of a propulsivecounterforce applied at the axle has over the lower wheel drag force. Asa result, aerodynamic trailer skirts in widespread use today areunnecessarily inefficient, since they generally extend below the levelof the axle.

Nevertheless, extended height trailer skirts have been shown to improvepropulsive efficiency, since they reduce the aerodynamic pressure on theupper wheel surfaces, which cause the vast majority of wheel drag andvirtually all of the loss in vehicle propulsive efficiency due to wheeldrag. However, the extended skirts shown in the art also impact theaerodynamic pressure on the lower wheel surfaces, where propulsivecounterforces delivered at the axle have a mechanical advantage overlower wheel drag forces.

As mentioned, diverting wind from impinging on the lower wheel surfacesactually increases overall vehicle drag, reducing propulsive efficiency.Deflecting wind from impinging on these lower wheel surfaces transfersthe aerodynamic pressure from these slower moving surfaces alsosuffering a mechanical disadvantage, to faster moving vehicle bodysurfaces having no mechanical advantage over propulsive counterforces,thereby increasing vehicle drag.

Nevertheless, numerous examples in the art demonstrate the currentpreference for aerodynamic skirts extending to below the level of theaxle. For example, in U.S. Pat. No. 7,942,471 B2, US 2006/0152038 A1,U.S. Pat. No. 6,974,178 B2, U.S. Pat. No. 8,303,025 B2, U.S. Pat. No.7,497,502 B2, U.S. Pat. No. 8,322,778 B1, U.S. Pat. No. 7,806,464 B2, US2010/0066123 A1, U.S. Pat. No. 8,342,595 B2, U.S. Pat. No. 8,251,436 B2,U.S. Pat. No. 6,644,720 B2, U.S. Pat. Nos. 5,280,990, 5,921,617,4,262,953, 7,806,464 B2, US 2006/0252361 A1, U.S. Pat. No. 4,640,541 allmake no mention of the differing relationships between upper wheel dragforces and lower wheel drag forces affecting vehicle propulsiveefficiency. Most of these patents depict figures showing skirtsextending well below the level of the axle. And an examination ofleading trailer skirt manufacturers shows the prevalence for extendedheight skirts currently for sale and needed to meet California carbonemission requirements.

Furthermore, a recent in-depth wind tunnel study sponsored the USDepartment of Energy and conducted at a pre-eminent research institutionof the United States government, Lawrence Livermore Laboratory waspublished Mar. 19, 2013, “Aerodynamic drag reduction of class 8 heavyvehicles: a full-scale wind tunnel study”, Ortega, et. al, and concludedthat trailer skirts are one of the most effective means to reduce dragon large tractor-trailer trucks. A large number of trailer skirtconfigurations were tested in this study, which employed traditionaltechniques for measuring total drag on the vehicle. Due to the nonlineareffects of upper wheel drag in rising headwinds, such techniques canproduce inaccurate measurements of gains in propulsive efficiency forvehicles having wheels exposed to headwinds. Thus, as yet this importantrelationship of upper wheel drag more predominately affecting overallvehicle drag—and especially over lower wheel drag which is oftencomparatively negligible and suffers a mechanical disadvantage againstpropulsive counterforces applied at the axle—has gone unrecognized.

And in the patent art cited above, several patents such as U.S. Pat.Nos. 4,262,953, 4,640,541, US 2006/0252361 A1, U.S. Pat. No. 7,806,464B2, U.S. Pat. No. 8,322,778 and others depict wind-deflecting panelsgenerally spanning the lateral width of the trailer, thereby inducingunnecessary drag by blocking air otherwise funneled between the wheels.Funneled air into the rear of the vehicle can reduce pressure drag onthe vehicle. In the art, there are numerous other examples of devicesattempting to enhance this vehicle drag reducing effect.

Finally, also in the cited art above, several patents such as US2010/0066123 A1, U.S. Pat. No. 8,342,595 B2 and U.S. Pat. No. 8,251,436B2 depict wind deflecting panels in front of the wheels of the trailerextending to well below the level of the axle, thereby inducingunnecessary vehicle drag by transferring drag from the slower movinglower wheel surfaces having a mechanical disadvantage, to the fastermoving vehicle body and frame. In the art, there are numerous otherexamples of devices attempting to enhance this wheel drag reducingeffect.

SUMMARY

All embodiments comprise either wind-deflecting skirts or panels for useon vehicles having wind-exposed wheels on a wheel assembly mountedunderneath the vehicle body, such as on the trailers of large commercialtrucks. Each embodiment is designed to deflect vehicle headwinds fromdirectly impinging on the upper wheel surfaces—the predominate draginducing surfaces on a wheel—and partially onto the lower wheelsurfaces—the least effective drag inducing surfaces on a wheel—therebyreducing vehicle drag and increasing vehicle propulsive efficiency. Eachembodiment is also ideally designed to keep lowermost wheel surfacesexposed to headwinds. Since propulsive counterforces applied at the axlehave a natural mechanical advantage over lower wheel drag forces,deflecting headwinds onto fully exposed lowermost wheels surfaces alsoincreases vehicle propulsive efficiency.

An embodiment comprises an inclined aerodynamic deflector panel assemblydesigned to deflect headwinds otherwise impinging on upper wheelsurfaces downward onto lower wheel surfaces of a trailing wheel set oneither side of the wheel assembly. The deflector panel assembly can be agenerally flat panel tilted to deflect air downward onto the lower wheelsurfaces, or a panel with perpendicular end plates projection forwardforming a U-shaped channel arranged to funnel air downward onto thelower wheel surfaces. The deflector panel assembly extends down from thevehicle body to no lower than the level of the axle of the wheelassembly, and may included wheel skirts covering the trailing wheelsets. The panel may also be extended across the lateral width of thetrailer to deflect headwinds below the trailing central axle assembly.

An embodiment comprises an aerodynamic skirt panel assembly designed todeflect headwinds otherwise impinging on upper wheel surfaces partiallydownward onto lower wheel surfaces of a trailing wheel set on eitherside of the wheel assembly. Toward the front end, the skirt panelassembly is located substantially inboard toward the centerline of thevehicle. Toward the rear end, the skirt panel assembly diverges rapidlyto the outside of the trailing wheel set in order to divert headwinds inpart onto the lower wheel surfaces. The ideal skirt assembly extendsdown from the vehicle body to no lower than the level of the axle infront of the wheel assembly, and may include wheel skirts covering thetrailing wheel sets.

An embodiment comprises a method for reducing the total drag-inducedresistive forces upon the wheel assembly as directed against the vehicleto reduce the required effective vehicle propulsive counterforce.

DESCRIPTION OF THE DRAWINGS

While one or more aspects pertain to most wheeled vehicles not otherwisehaving fully shielded wheels that are completely protected from oncomingheadwinds, the embodiments can be best understood by referring to thefollowing figures.

In FIG. 1, an inclined aerodynamic deflector panel assembly is mountedunderneath the trailer of an industrial truck in front of a wheel set ofthe rear wheel assembly and rearward of the forward landing gear.

In FIG. 2, the inclined aerodynamic wheel deflector panel assembly ofFIG. 1 is shown mounted on the trailer as viewed in cross-section fromthe front of the vehicle. Two deflector panel assemblies are shown, eachas mounted in front of one of the wheel sets of the rear wheel assembly.

In FIG. 3, an inclined aerodynamic deflector panel assembly, whichappears in side view similar to as shown in FIG. 1, is shown mounted onthe trailer as viewed in cross-section from the front of the vehicle.

In FIG. 4, a channeled aerodynamic deflector panel assembly is mountedunderneath the trailer of an industrial truck in front of the rear wheelassembly.

In FIG. 5, the channeled aerodynamic wheel deflector panel assembly ofFIG. 4 is shown mounted on the trailer as viewed in cross-section fromthe front of the vehicle. Two deflector panel assemblies are shown, eachas mounted in front of one of the wheel sets of the rear wheel assembly.

In FIG. 6, the channeled aerodynamic deflector panel assembly, whichappears in side view similar to as shown in FIG. 4, is shown mounted onthe trailer as viewed in cross-section from the front of the vehicle.

In FIG. 7, a channeled aerodynamic deflector panel and wheel skirtassembly is mounted underneath the trailer of an industrial truck infront of a wheel set of the rear wheel assembly.

In FIG. 8, an aerodynamic wheel deflector panel is mounted underneaththe trailer of an industrial truck in front of a wheel set of the rearwheel assembly.

In FIG. 9, an aerodynamic deflector panel and wheel skirt assembly ismounted underneath the trailer of an industrial truck in front of therear wheel assembly.

In FIG. 10, an aerodynamic deflector skirt assembly is mountedunderneath the trailer of an industrial truck in front of the rear wheelassembly.

In FIG. 11, the aerodynamic deflector skirt assembly of FIG. 10 is shownfrom below the vehicle.

In FIG. 12, the aerodynamic deflector skirt assembly together with awheel skirt panel assembly is mounted to the trailer of an industrialtruck.

FIG. 13 is a front cycle wheel assembly, as typically found on a bicycleor motorcycle, where a fairing is attached and positioned as shown toeach interior side of the fork assembly, thereby shielding the upper-and front-most surfaces of the spoked wheel from oncoming headwinds.

FIG. 14 is a series of curves showing the results of an analysis of thedrag mechanics on a bicycle with shielded upper wheels, indicating thata bicycle with shielded upper wheels is faster when facing headwinds.Several curves are displayed, as examples of different bicycles eachhaving a different proportion of wheel-drag to total-vehicle-drag.

FIG. 15 shows a plot of calculated average moments—about the groundcontact point of drag force, that are exerted upon rotating wheelsurfaces as a function of the elevation above the ground. The relativedrag forces are determined from calculated wind vectors for the rotatingsurfaces on a wheel moving at a constant speed of V, and plotted forseveral different wind and wheel-surface shielding conditions.Specifically, relative magnitudes in average drag moments about theground contact point as a function of elevation are plotted, for eightconditions: comparing with (dashed lines) and without (solid lines)shielding covering the upper third of wheel surfaces, for tailwindsequal to half the vehicle speed; for null headwinds; for headwinds equalto half the vehicle speed; and for headwinds equal to the vehicle speed.The rising solid curves plotted show the highest moments to be near thetop of the wheel, while the dashed curves show the effect of the uppershield in substantially reducing the average drag moments on therotating wheel.

FIG. 16 shows a plot of calculated relative drag torque exerted uponrotating wheel surfaces as a function of elevation above the ground. Therelative total drag torques are determined from the calculated averagemoments in combination with the chord length at various elevations on awheel moving at a constant speed of V, for several different wind andwheel-surface shielding conditions. Relative magnitudes in total dragtorque about the ground contact point as a function of elevation areplotted for eight conditions: comparing with (dashed lines) and without(solid lines) shielding covering the upper third of wheel surfaces, fortailwinds equal to half the vehicle speed; for null headwinds; forheadwinds equal to half the vehicle speed; and for headwinds equal tothe vehicle speed. The areas under the plotted curves represent thetotal torque from frictional drag on wheel surfaces. Comparing thedifferences in area under the plotted curves reveals the general trendof the upper shield to substantially reduce the total drag torque on therotating wheel.

FIG. 17 (Prior Art) is a diagram of a wheel rolling on the groundrepresenting typical prior art models, showing the net pressure dragforce (P) exerted upon the forward wheel vertical profile—which moves atthe speed of the vehicle—being generally centered near the axle of thewheel and balanced against the propulsive force (A) applied at the axle.

FIG. 18 is a diagram of a wheel rolling on the ground, showing the netfriction drag force (F) upon the wheel surfaces—which move at differentspeeds depending on the elevation from the ground—being offset from theaxle and generally centered near the top of the wheel. A ground reactionforce (R)—arising due to the drag force being offset near the top of thewheel—is also shown. The force (A) applied at the axle needed toovercome the combination of drag forces (F+P) and reaction force (R) isalso shown.

In FIG. 19, an inclined aerodynamic deflector panel and wheel skirtassembly is mounted underneath the trailer of an industrial truck.

In FIG. 20, an aerodynamic wheel skirt panel is shown attached the frameof a semi truck tractor. The wheel skirt panel is disposed to shieldupper tire sidewalls of the rearward wheels of the truck tractor fromheadwinds otherwise impinging thereon.

DESCRIPTION OF WHEEL DRAG MECHANICS

As mentioned, drag force on exposed wheels increases more rapidly onupper wheel surfaces than on vehicle frame surfaces, causing anon-linear relation from rising wind speeds between net drag forces onvehicle frame surfaces versus net drag forces on vehicle wheel surfaces.Thus, vehicles having wind-exposed wheels are particularly sensitive toexternal headwinds reducing propulsive efficiency. As a result, thereexists a need for an improved aerodynamic deflector and skirt for use onindustrial trucks and trailers.

Because of this rising dominance of wheel drag in rising headwinds—dueto the non-linear relation from rising wind speeds between net dragforces on vehicle frame surfaces versus net drag forces on vehicle wheelsurfaces—a discussion of the wheel drag mechanics central to thisnon-linear relationship is presented herein. The upper wheel fairing isdescribed below as a simple solution for reducing vehicle drag in risingheadwinds on a cycle, and is presented herein as background for thepresent embodiment.

The shielding provided by fairing 1 in FIG. 11 is particularly effectivesince aerodynamic forces exerted upon exposed vehicle surfaces aregenerally proportional to the square of the effective wind speedimpinging thereon. Moreover, the power required to overcome these dragforces is generally proportional to the cube of the effective windspeed. Thus, it can be shown that the additional power required toovercome these drag forces in propelling a vehicle twice as fast over afixed distance, in half the time, increases by a factor of eight. Andsince this power requirement is analogous to rider effort—in the case ofa bicycle rider—it becomes critical to shield the most criticaldrag-inducing surfaces on a vehicle from oncoming headwinds.

FIG. 14 shows the results of an analysis of the drag mechanics on abicycle with shielded upper wheels. The curves indicate that a bicyclewith shielded upper wheels is faster when facing headwinds. Moreover,the gains in propulsive efficiency are shown to quickly increase in onlya modest headwind, but continue to rise as headwinds increase further.

In any wheel used on a vehicle, and in the absence of any externalheadwinds, the effective horizontal wind speed at a point on the wheelat the height of the axle is equal to the ground speed of the vehicle.Indeed, the effective headwind speed upon any point of the rotatingwheel depends on that point's current position with respect to thedirection of motion of the vehicle.

Notably, a point on the moving wheel coming into direct contact with theground is necessarily momentarily stationary, and therefore is notexposed to any relative wind speed, regardless of the speed of thevehicle. While the ground contact point can be rotating, it is nottranslating; the contact point is effectively stationary. And points onthe wheel nearest the ground contact point are translating with onlyminimal forward speed. Hence, drag upon the surfaces of the wheelnearest the ground is generally negligible.

Contrarily, the topmost point of the wheel assembly (opposite theground) is exposed to the highest relative wind speeds: generally atleast twice that of the vehicle speed. And points nearest the top of thewheel are translating with forward speeds substantially exceeding thevehicle speed. Thus, drag upon the surfaces of the upper wheel can bequite substantial.

Lower points on the wheel are exposed to lesser effective wind speeds,approaching a null effective wind speed—and thus negligible drag—forpoints nearest the ground.

Importantly, due to the rotating geometry of the wheel, it can be shownthat the effective combined frictional drag force exerted upon the wheelis typically centered in closer proximity to the top of the wheel,rather than centered closer to the axle as has been commonly assumed inmany past analyses of total wheel drag forces. While the net pressure(or form) drag (P) force on the forwardly facing profile of the wheel isgenerally centered with elevation and directed near the axle on thewheel (as shown in FIG. 17), the net frictional drag force (F) upon themoving surfaces is generally offset to near the top of the wheel (asshown in FIG. 18).

Indeed, it is near the top of the wheel where the relative winds areboth greatest in magnitude, and are generally oriented most directlyopposed to the forward motion of rotating wheel surfaces. Moreover, inthe absence of substantial external headwinds, the frictional dragexerted upon the lower wheel surfaces contributes relatively little tothe net drag upon the wheel, especially when compared to the drag uponthe upper surfaces. The combined horizontal drag forces (from pressuredrag from headwinds deflected by both the leading and trailing wheelforwardly facing profiles, and from frictional drag from headwindsimpinging upon the forwardly moving surfaces) are thus generallyconcentrated near the top of the wheel under typical operatingconditions. Moreover, with the faster relative winds being directedagainst the uppermost wheel surfaces, total drag forces combine near thetop to exert considerable retarding torque upon the wheel.

As mentioned, the horizontal drag forces are primarily due to bothpressure drag forces generally distributed symmetrically across theforwardly facing vertical profiles of the wheel, and to winds infrictional contact with moving surfaces of the wheel. Pressure dragforces arise primarily from the displacement of air from around theadvancing vertical profile of the wheel, whose circular outline moves atthe speed at the vehicle. As discussed above, since the entire circularprofile moves uniformly at the vehicle speed, the displacement of airfrom around the moving circular profile is generally uniformlydistributed with elevation across the forwardly facing vertical profileof the wheel. Thus, these pressure drag forces (P, as shown in FIG. 17and FIG. 18) are also generally evenly distributed with elevation acrossthe entire forwardly facing vertical profile of the wheel, and centerednear the axle. And these evenly distributed pressure drag forces arisegenerally in proportion only to the effective headwind speed of thevehicle.

Frictional drag forces (F, as shown FIG. 18), however, are concentratednear the top of the wheel where moving surfaces generally exceed vehiclespeed—while the lower wheel surfaces move at less than the vehiclespeed. Since drag forces are generally proportional to the square of theeffective wind speed, it becomes apparent that with increasing windspeed, that these upper wheel frictional drag forces directed upon themoving surfaces increase much more rapidly than do pressure drag forcesdirected upon the forward profile of the wheel. Indeed, these frictiondrag forces generally arise in much greater proportion to an increasingeffective headwind speed of the vehicle. Nevertheless, these increasedfrictional drag forces being directed on the upper wheel is only apartial factor contributing to augmented wheel drag forces beingresponsible for significantly retarded vehicle motion.

Significantly, both types of drag forces can be shown to exert momentsof force pivoting about the point of ground contact. And as such, eithertype of drag force exerted upon the upper wheel retards vehicle motionconsiderably more than a similar force exerted upon a substantiallylower surface of the wheel. Minimizing these upper wheel drag forces istherefore critical to improving propulsive efficiency of the vehicle.

Also important—and due to the rotating geometry of the wheel—it can beshown that the vehicle propulsive force on the wheel appliedhorizontally at the axle must substantially exceed the net opposing dragforce exerted near the top of the wheel. These forces on a wheel areactually leveraged against each other, both pivoting about the samepoint—the point on the wheel which is in stationary contact with theground—and which is constantly changing lateral position with wheelrotation. Indeed, with the geometry of a rolling wheel momentarilypivoting about the stationary point of ground contact, the lateral dragand propulsive forces each exert opposing moments of force on the wheelcentered about this same point in contact with the ground.

Furthermore, unless the wheel is accelerating, the net torque from thesecombined moments on the wheel must be null: The propulsive momentgenerated on the wheel from the applied force at the axle mustsubstantially equal the opposing moment from drag forces centered nearthe top of the wheel (absent other resistive forces, such as bearingfriction, etc.). And the propulsive moment generated from the appliedforce at the axle has a much shorter moment arm (equal to the wheelradius) than the opposing moment from the net drag force centered nearthe top of the wheel (with a moment arm substantially exceeding thewheel radius)—since both moment arms are pivoting about the samestationary ground contact point. Thus, for these opposing moments toprecisely counterbalance each other, the propulsive force applied at theaxle—with the shorter moment arm—must substantially exceed the net dragforce near the top of the wheel.

In this way, the horizontal drag forces exerted upon the upper surfacesof the wheel are leveraged against opposing and substantially magnifiedforces at the axle. Hence, a relatively small frictional drag forcecentered near the top of the wheel can have a relatively high impact onthe propulsive counterforce required at the axle. Shielding these upperwheel surfaces can divert much of these headwind-induced drag forcesdirectly onto the vehicle body, thereby negating much of the retardingforce amplification effects due to the pivoting wheel geometry.

Moreover, since the propulsive force applied at the axle exceeds thecombined upper wheel drag forces, a lateral reaction force (R, as shownin FIG. 18) upon the wheel is necessarily developed at the groundcontact point, countering the combined unbalanced propulsive and dragforces on the wheel: Unless the wheel is accelerating, the reactionforce at the ground, together with the upper wheel net drag forces(F+P), combine (A=F+R+P, as shown in FIG. 18) to countervail the lateralpropulsive force (A) applied at the axle. This reaction force istransmitted to the wheel through frictional contact with the ground. Inthis way, an upper wheel drag force is further magnified against theaxle. For these multiple reasons, it becomes crucial to shield the upperwheel surfaces from exposure to headwinds.

Given that the propulsive force (A) applied at the axle must overcomeboth the net wheel drag forces (F+P) and the countervailing lowerreaction force (R) transmitted through the ground contact point, it canbe shown that the net drag force upon the upper wheel can oppose vehiclemotion with nearly twice the sensitivity as an equivalent drag forceupon the static frame of the vehicle. Hence, shifting the impact ofupper wheel drag forces to the static frame can significantly improvethe propulsive efficiency of the vehicle.

Furthermore, as drag forces generally increase in proportion to thesquare of the effective wind speed, the more highly sensitive upperwheel drag forces increase far more rapidly with increasing headwindspeeds than do vehicle frame drag forces. Thus, as the vehicle speedincreases, upper wheel drag forces rapidly become an increasingcomponent of the total drag forces retarding vehicle motion.

And given the greater sensitivity of speed-dependent upper wheel dragforces—as compared against vehicle frame drag forces—to the retarding ofvehicle motion, considerable effort should first be given to minimizingupper wheel drag forces. And shielding the faster-moving uppermostsurfaces of the wheel assembly from oncoming headwinds, by using thesmallest effective fairing assembly, is an effective means to minimizeupper wheel drag forces.

Contrarily, drag forces on the lower wheel generally oppose vehiclemotion with reduced sensitivity compared to equivalent drag forces onthe static frame of the vehicle. Propulsive forces applied at the axleare levered against lower wheel drag forces, magnifying their impactagainst these lower wheel forces. Shielding lower wheel surfaces cangenerally negate this mechanical advantage, and can actually increaseoverall drag on the vehicle.

Moreover, as discussed above, headwinds on the static frame generallyexceed the speed of winds impinging on the lower surfaces of the wheel.Hence, frictional drag forces on the lower wheel surfaces are greatlyreduced. Thus, it is generally counterproductive to shield the wheelbelow the level of the axle. Drag on a vehicle is generally minimizedwith upper wheel surfaces shielded from headwinds and with lower wheelsurfaces exposed to headwinds.

Wheel drag sensitivity to retarding vehicle motion becomes even moresignificant in the presence of external headwinds. With externalheadwinds, the effective wind speed impinging on the critical upperwheel surfaces can well exceed twice the vehicle speed. Shieldingprotects the upper wheel surfaces both from external headwinds, and fromheadwinds due solely to vehicle motion.

Indeed, wheel surfaces covered by the shield are exposed to winds duesolely to wheel rotation; headwinds are deflected. The effective dragwinds beneath the shield are generally directed tangentially to rotatingwheel surfaces, and vary in proportion to radial distance from the axle,reaching a maximum speed at the wheel rim equal to the vehicle speed,regardless of external headwinds. Since drag forces vary generally inproportion to the square of the wind speed, the frictional drag forcesare considerably reduced on shielded upper wheel surfaces. Using thesewind shields, shielded wheel surfaces are exposed to substantiallyreduced effective wind speeds—and to generally much less than half ofthe drag forces without shielding.

Diminished drag forces from external headwinds impinging on the slowermoving lower surfaces of a rolling wheel generally oppose wheel motionwith much less retarding torque than drag forces from winds impinging onthe faster upper surfaces. Indeed, tests demonstrate that with uppershields installed on a suspended bicycle wheel, the wheel will spinnaturally in the forward direction when exposed to headwinds. Withoutthe shields installed, the same wheel remains stationary when exposed toheadwinds, regardless of the speed of the headwind. And an unshieldedspinning wheel will tend to stop spinning when suddenly exposed to aheadwind. This simple test offers an explanation for the unexpectedresult and demonstrates that by minimally shielding only the upper wheelsurfaces from external headwinds, the overall drag upon the rotatingwheel can be substantially reduced.

Furthermore, as external headwinds upon a forwardly rotating vehiclewheel add relatively little frictional drag to the lower wheelsurfaces—which move forward at less than the vehicle speed—but add farmore significant drag to the upper wheel surfaces, which move forwardfaster than the vehicle speed and which can more significantly retardvehicle motion, shielding the upper wheel surfaces against headwinds isparticularly beneficial. Since drag forces upon the wheel are generallyproportional to the square of the effective wind speed thereon, and theadditional drag on the wheel—and thereby on the vehicle—increasesrapidly with headwinds, shielding these upper surfaces greatly reducesthe power required to propel the vehicle. Moreover, the relativeeffectiveness of shielding upper wheel surfaces generally increases withincreasing headwinds.

An examination of the retarding wind vectors on a rotating wheel canreveal the large magnitude of drag retarding moments upon the uppermostwheel surfaces, relative to the lower wheel surfaces. And an estimate ofthe frictional drag torque on the wheel can be determined by firstcalculating the average moments due to drag force vectors at variouspoints—all pivoting about the ground contact point—on the wheel (resultsshown plotted in FIG. 15), and then summing these moments at variouswheel elevations above the ground and plotting the results (FIG. 16).The area under the resulting curve (shown in FIG. 16 as a series ofcurves representing various headwind conditions) then represents thetotal frictional drag (absent profile drag) torque upon the wheel.

In order to determine the relationship between this torque and elevationon the wheel, the magnitudes of the drag wind vectors that areorthogonal to their corresponding moment arms pivoting about the pointof ground contact must first be determined. These orthogonal vectorcomponents can be squared and then multiplied by the length of theircorresponding moment arms, in order to determine the relative momentsdue to drag at various points along the wheel rim.

The orthogonal components of these wind vectors tend to increaselinearly with elevation for points on the rim of the wheel, and also forpoints along the vertical mid-line of the wheel. Calculating the momentsalong the vertical mid-line of the wheel can yield the minimum relativedrag moments at each elevation. Calculating an average of the maximumdrag moment at the rim combined with the minimum drag moment along themid-line can then yield the approximate average drag moment exerted ateach elevation upon the wheel. Multiplying this average drag moment bythe horizontal rim-to-rim chord length can yield an estimate of the dragtorque exerted upon the wheel at each elevation level (FIG. 16). Thesecalculations are simply determined from the geometry of the rotatingwheel; the object of this analysis is to determine the likely relativemagnitudes of drag torques upon the wheel at various elevations.

From the resulting plots (FIG. 16), it can be estimated that theuppermost approximate one-third section of the wheel likely contributesmost of the overall drag torque upon the wheel. Thus, by shielding thisupper section from headwinds, drag torque can be considerably reduced.With upper-wheel shielding, as noted above, the relative winds beneaththe shield are due mostly to wheel rotation, and are generally directedtangentially to the wheel. The resulting drag torque under the shieldedsections can then be determined as above, and compared with theunshielded drag torque for similar headwind conditions.

These calculations—generally confirmed by tests—indicate a substantialreduction in retarding drag torque upon the shielded upper wheelsurfaces. In the absence of external headwinds, the plots of FIG. 16indicate that shielding the uppermost approximate one-third section ofthe wheel can reduce the drag torque of this section considerably, by asmuch as 75 percent. Moreover, repeating calculations and testing with anexternal headwind equal to the vehicle speed indicates that upper wheelshielding can reduce the comparative upper wheel drag torque of thissection by still more, perhaps by as much as 90 percent. Hence, thepotential effectiveness of shielding upper wheel surfaces can besignificant, especially with surfaces having higher drag sensitivities,such as wheel spoke surfaces.

As discussed above, since upper wheel drag forces are leveraged againstthe axle—thereby magnifying the propulsive counterforce required at theaxle—an increase in drag force on the wheels generally retards vehiclemotion much more rapidly than does an increase in other vehicle dragforces. And while under external headwind conditions, the total drag ona vehicle with wheels exposed directly to headwinds increases still morerapidly with increasing vehicle speed.

Shielding upper wheel surfaces effectively lowers the elevation of thepoint on the wheel where the effective net drag force is exerted,thereby diminishing the magnifying effect of the propulsive counterforcerequired at the axle, as discussed above. As a result, the reduction indrag force upon the vehicle achieved by shielding the upper wheelsurfaces is comparatively even more significant with increasing externalheadwinds. Shielding these upper wheel surfaces can thereby improverelative vehicle propulsion efficiency under headwinds by an evengreater margin than under null wind conditions.

Moreover, shielding these upper wheel surfaces can be particularlybeneficial to spoked wheels, as round spokes can have drag sensitivitiesmany times greater than that of more streamlined surfaces. As roundspokes—in some configurations—can have drag coefficients ranging fromone to two orders of magnitude greater than corresponding smooth,streamlined surfaces, shielding the spokes of the upper wheel fromexternal wind becomes particularly crucial in reducing overall drag uponthe wheel.

Accordingly—given these multiple factors—a relatively small streamlinedfairing attached to the vehicle structure and oriented to shield theupper surfaces of the wheel assembly from oncoming headwindssubstantially reduces drag upon the wheel, while minimizing total dragupon the vehicle. Consequently, an embodiment includes the addition ofsuch a fairing to any wheeled vehicle—including vehicles having spokedwheels, where the potential drag reduction can be even more significant.

The addition of such minimal fairings to each side of a traditionalspoked bicycle wheel, for example, reduces windage losses and improvespropulsive efficiency of the bicycle, particularly at higher cyclespeeds or in the presence of headwinds, while minimizing cycleinstability due to crosswind forces. Since crosswinds are a significantfactor restricting the use of larger wheel covers, minimizing thefairing size is also an important design consideration. And minimizingform drag induced by the forward-facing profile of the fairing also willinfluence the fairing design. The preferred fairing size will likelysubstantially cover the upper section of the exposed wheel, and beplaced closely adjacent to the wheel surfaces, consistent with generaluse in bicycles. In heavier or powered cycles, design considerations maypermit somewhat larger fairings, covering even more of the wheelsurfaces.

As shielding upper wheel surfaces can reduce overall drag on thevehicle, while simultaneously augmenting the total frontal profile areaof the vehicle exposed to headwinds, a natural design constraint emergesfrom these competing factors: Shields should be designed sufficientlystreamlined and positioned sufficiently close to wheel surfaces toprovide reduced overall vehicle drag. And as shielding effectivenesspotentially increases under headwind conditions, shields designed withlarger surface areas and larger frontal profiles may still providereduced overall vehicle drag under headwind conditions, if not undernull wind conditions. Thus, a range of design criteria may be applied toselecting the best configuration and arrangement of the fairing, andwill likely depend on the particular application. In any particularapplication, however, the embodiment will include a combination ofdesign factors discussed above that will provide a reduction in overallvehicle drag.

In a cycle application, for example, fairings positioned within thewidth of the fork assembly will likely provide the most streamlineddesign which both shields spokes from headwinds but also minimizes anyadditional form drag profile area to the vehicle frame assembly. Inother applications, insufficient clearances may preclude positioning thefairings immediately adjacent to moving wheel surfaces. In suchsituations, headwinds may be sufficient in magnitude to cause areduction in overall vehicle drag to justify the use of wider upperwheel fairings—positioned largely outside the width of the forkassembly—with extended forward profile areas.

Furthermore, from the previous analysis a consideration the drag torquecurves wholly above the level of the axle, it becomes apparent thatshielding the wheel is best centered about an elevation likely between75 and 80 percent of the diameter of the wheel, or near the center ofthe area under the unshielded torque curve shown in FIG. 16. While dragforces are generally greatest in magnitude near the top of the wheel,the effective exposed topmost surface areas are much smaller, therebylimiting the magnitude of drag torques upon the uppermost surfaces ofthe wheel. Thus, the upper wheel fairing would best extend above andbelow this critical level (generally, between 75 and 80 percent of thediameter of the wheel) in order to optimally minimize drag upon thewheel. And as the surfaces forward of the axle are the first to beimpacted by headwinds, shielding these surfaces is essential todeflecting headwinds from the rearward surfaces. Thus, thehigher-sensitivity drag-inducing surfaces in the forward upper quadrantand centered about this critical elevation on the wheel generally needto be shielded for optimal minimization of drag. Thesehigher-sensitivity drag-inducing surfaces generally centered about thiscritical elevation and extending to include those surfaces with higherdrag-inducing sensitivities that are positioned mostly in the forwardupper quadrant of the wheel, but likely also to include much of thewheel surfaces positioned in the rearward upper quadrant, are hereindefined and later referred to as: major upper drag-inducing surfaces.And the critical level about which the major drag-inducing surfaces aregenerally centered in elevation is herein defined and later referred toas: critical elevation.

As discussed, the precise elevation about which the major upperdrag-inducing surfaces are centered, as well as the precise extent towhich surfaces in the forward quadrant and in the upper half of thewheel are included in the major upper drag-inducing surfaces, willdepend on the particular application and operating conditions. Certainwheel surfaces with higher drag sensitivities, such as wheel spokes,generally need to be shielded when positioned within the region of themajor upper drag-inducing surfaces. Other surfaces such as smooth tiresurfaces having lower drag sensitivities may also benefit from shieldingif their surface areas are extensive, are positioned near the criticallevel in elevation, or are the primary upper wheel surfaces exposed toheadwinds. In the example analysis of FIGS. 15 and 16, a uniform surfaceacross the wheel having a constant drag-sensitivity was assumed. In anyparticular application, the unique combination of different wheelsurfaces with differing drag sensitivities will determine the particularheight of the critical elevation level about which the major upperdrag-inducing surfaces are centered.

A similar analysis can be performed for form drag forces on the movingforward vertical profiles of the wheel rim or tire. The results obtainedare generally similar in form, though may differ somewhat in magnitudesas the effective wind speeds on the moving profiles are generally loweron the upper wheel—equal to the vehicle speed—and will depend on theparticular application, including the total area of the wheel forwardprofile exposed to headwinds, and to headwind and vehicle speeds.Nevertheless, the net pressure drag torque caused by the moving outlineof the wheel is also centered above the level of the axle, and therebymerits consideration in determining the particular height of thecritical elevation level, and in the ultimate configuration of thefairing.

Hence, the fairing shown in FIG. 13 is best configured to shield theuppermost and forward wheel surfaces, and to extend rearward to at leastpartially shield the forward profile of the trailing portion of theupper wheel rim, consistent with the further requirement to extenddownward as much as practical to the level of the axle. As mentioned,crosswind considerations will also influence the ultimate configurationfor a particular application.

In consideration of further embodiments described below, the operatingprinciples described above will generally apply, and may be referredthereto.

DETAILED DESCRIPTION

Various embodiments are described below in detail, each providing meansto deflect headwinds from directly impinging on the upper wheelsurfaces, thereby reducing vehicle drag and increasing propulsiveefficiency.

First Embodiment—FIGS. 1 and 2

As shown in FIGS. 1 and 2, an embodiment comprises an inclinedaerodynamic wheel deflector panel assembly 20 attached to and mountedunderneath the body of a trailer 16 for a commercial vehicle. Theinclined wheel deflector panel assembly 20 is located forward of therear wheel assembly 17 and located directly in front of a trailing wheelset 18 which would otherwise be exposed to headwinds when the vehicle isin forward motion. The inclined wheel deflector panel assembly 20 isplanar in shape, mounted inclined in a forwardly-angled orientation withthe upper edge more forwardly located and the lower surface located morerearward on the vehicle. The inclined wheel deflector panel assembly 20spans the lateral width of the trailing wheel set 18 of the trailingrear wheel assembly 17 located on either side of the vehicle. Theoptimal inclined wheel deflector panel assembly 20 extends downwardideally to no lower than the level of the axle 19 and is locatedproximal to the trailing wheel set 18 in order to deflect upper wheelheadwinds onto the exposed lower wheel surfaces.

It can be concluded from the discussion of wheel drag mechanics above,that since propulsive counterforces applied to the wheel at the axlehave a mechanical advantage over lower wheel drag forces—which arenecessarily applied to the wheel below the level of the axle—directingupper wheel headwinds onto the lower wheel surfaces can significantlyreduce overall vehicle drag and improve propulsive efficiency. Thereasons for these gains in vehicle efficiency become apparent by furtherconsidering how wheel drag forces compare with vehicle body drag forces.

As discussed earlier, drag forces on the wheel must be countered by apropulsive force from the vehicle body applied at the axle. And it canbe established that drag forces on the upper wheel have a mechanicaladvantage over countervailing propulsive counterforces applied at theaxle. And with the wheel deflector assembly attached to the vehiclebody, drag on the deflector must also be countervailed by a propulsivecounterforce applied to the vehicle body at a propulsive axle.

Thus, in order to determine the relative difference in total vehicledrag between the traditional extended height deflector divertingheadwinds from impinging on both the upper and the lower wheels, and theimproved reduced height deflector with the lower wheel surfaces ideallyfully exposed to headwinds, the added vehicle drag derived from thesurface of the deflector panel extending below the level of the axlemust be compared against the vehicle drag arising from the correspondingadditional surfaces of the lower wheel otherwise shielded by theextended deflector. And as already established above, the relativeeffects of these resistive forces on vehicle propulsion are non-linearlyrelated, and vary considerably with increasing headwinds: for vehiclesfacing faster external headwinds the nonlinear effects quickly increase,as discussed above and as shown in FIG. 14, where the results of ananalysis of the drag mechanics of a bicycle facing increasing headwindsshows rapid increases in propulsive efficiency by shielding the upperwheels.

A skilled artisan will recognize from the curves shown FIG. 14 that asthe relative external headwind increases on the vehicle, so does theincrease in propulsive efficiency of the vehicle. And a skilled artisanwill also recognize that the natural design constraint described abovefor the cycle wheel fairing of FIG. 13 similarly applies to the winddeflecting fairing of the present embodiment.

This inherent design constraint implies that for a given vehicle under agiven relative external headwind condition—as shown along the horizontalaxis of the plots in FIG. 14—a wind-deflecting fairing of the presentembodiment will similarly be constrained to have a limited overallwind-deflecting extent that will produce a reduction in overall vehicledrag. This limited wind-deflecting extent includes a limit on the totaldrag-inducing surface area extent of the wind-deflecting fairing,including a combined limit in both forward and downward extension offairing surfaces.

And as discussed extensively above for the cycle wheel fairing of FIG.13, the relative effects of drag forces on the fairing versus drag onthe various points on the wheel are not simply related. Instead, thedrag forces on various points on the wheel are magnified or de-magnifiedas applied against the axle, whereas the drag on either the cyclefairing or on the similar drag-inducing surfaces of the wind-deflectingfairing of the present embodiment are directly applied equivalentlyagainst the same axle.

Thus, since propulsive counterforces applied at the axle have amechanical advantage over drag forces on the lower wheel surfaces, asimple comparison of the net drag force on either surface alone—eitheron the lower wheel or on the extended deflector surface—is entirelyinsufficient to determine the relative effect each has on vehiclepropulsive efficiency. Instead, the magnitudes of the drag force fromeach surface must be reflected to an equivalent force applied at thesame axle and compared against one another.

For the lower wheel surfaces, the net drag force as applied against theaxle is diminished by leveraging about the point of ground contact, aspreviously discussed. For the lower deflector panel surface, the dragforce is directed against the axle without magnification since it istransmitted directly through the body and frame of the vehicle. Althoughanother axle of the vehicle may be the used as the propulsive axle, thetwo net drag forces must be compared against each other as reflected atthe same affected axle in order to gauge their relative effects onoverall vehicle drag.

For the lower deflector surface, the drag force on the surface is—likeother vehicle body drag forces—directly countervailed by the propulsivecounterforce applied at the driven axle. For the lower wheel surfaces,the situation is more complicated due both to the mechanical advantagethat the propulsive forces have over lower wheel drag forces, and to theeffects that the summation moments of drag force (FIG. 15) at differentpoints on the rotating wheel have on the net lower wheel drag force.

As noted earlier under the Description of Wheel Drag Mechanics, and asshown in the plot of FIG. 16, the average drag torque exerted againstthe lower wheel surfaces has far less impact on the total wheel drag asexerted upon the vehicle than does the average drag torque exertedagainst the upper wheel surfaces. This is due largely to the pivotinggeometry of the rotating wheel, where wheel forces are levered about thesame stationary point of ground contact at the bottom of the wheel.Owing in part to their longer moment arms, drag forces applied to theupper wheel produce far greater resistive torques on the wheel than dodrag forces applied to the lower wheel.

Consequently, drag forces on the upper wheel surfaces are ideallyshifted to the lower wheel surfaces in order to benefit the propulsiveefficiency of the vehicle. As a result, deflecting headwinds from theupper wheel surfaces onto the lower wheel surfaces can substantiallyreduce overall vehicle drag and improve propulsive efficiency.

And in the case of industrial trucks having large wheels with largertires, the relative effects of resistive pressure drag forces on thewheel over frictional drag forces is exacerbated over that of a spokedbicycle wheel as described above in the discussion of the wheel dragmechanics. As mentioned, the spoked wheels with thin tires and rims usedon a bicycle can produce significant frictional drag effects resistingvehicle propulsion. Trucks with smooth wheels and tires are moresignificantly affected by pressure drag forces acting against the upperwheel forward-facing profile surfaces, than are bicycles with thin tiresand rims.

Thus for trucks, deflecting upper wheel headwinds downward onto thelower wheel becomes an important operating function. Since propulsivecounterforces at the axle have a mechanical advantage over lower wheeldrag forces applied to the wheel below the level of the axle, deflectingheadwinds downward onto the lower wheel can reduce overall vehicle dragand improve propulsive efficiency.

The natural design constraint method discussed above can also be used incombination with an accounting for the non-linear effects on vehicledrag from drag forces directed on various points on the wheel todetermine the limited extent of the wind-deflecting fairing of thepresent embodiment that will also yield an overall reduction in vehicledrag, including the combined limit in both forward and downward extentof the fairing. And as is evident from the curves of FIG. 14, thecombined limit for the overall drag-inducing extent of thewind-deflecting fairing of the present embodiment will vary with bothvehicle configuration and relative external headwind condition.

From an examination of the curves of FIG. 14, it becomes evident thatthe worst-case limit for the overall extent of the fairing is while thevehicle is operated under null wind conditions, where the relative gainsin vehicle efficiency are comparatively minimal, and as shown at theleft vertical axis of the plots of FIG. 14. As the relative externalheadwind increases, the relative gains in vehicle efficiency quicklyincrease, as shown in the general trend of the efficiency curves risingtoward the right side of the plots.

Therefore, a skilled artisan then will understand that the mostrestrictive limit for the overall extent of the fairing will be whilethe vehicle is operated under null external headwinds conditions. If theextent of the fairing is sufficiently limited to produce an overallreduction in vehicle drag under null operating conditions, then the thuslimited fairing will also produce even more gains in vehicle efficiencyunder an external headwind condition.

And from the discussion above, it becomes evident that the fairing couldbe designed either to be more limited in forward extent and moreextensive in downward extent or alternatively could be designed insteadto be more extensive in forward extent and more limited in downwardextent, and still produce the same measure of gains in overall vehiclepropulsive efficiency.

Thus, the fairing could be designed to be somewhat limited in forwardextent and to extend somewhat below the level of the axle while stillyielding a reduction in overall vehicle drag, especially while thevehicle is operated under a substantial relative external headwindcondition. This potential configuration for the fairing becomes quiteevident both from an examination of the curves of FIG. 16, and from aconsideration of how the very limited mechanical disadvantage thatsurfaces of the wheel located not very far below the level of the axlehave over vehicle frame drag forces, such as wheel fairing or deflectordrag forces.

Indeed, FIG. 16 shows that near the level of the axle, much lessrelative gains in propulsive efficiency are gained from shielding morecentrally located wheel surfaces in elevation than from shielding theuppermost wheel surfaces positioned substantially above the axle nearthe critical elevation. And FIG. 16 also shows that the relative gainsin vehicle efficiency increase in rising relative external headwinds.

While the ideal configuration of the fairing includes a limit forfairing surfaces to extend downward to lower than the level of the axle,the discussion above makes clear that this is optimal limitation is notfully restrictive. Instead, a skilled artisan would recognize that awind-deflecting fairing of the present embodiment could be designed tobe somewhat limited in forward extent while also extending somewhatbelow the level of the axle while still yielding a reduction in overallvehicle drag, especially while the vehicle is operated under a varietyof relative external headwind conditions.

Or alternatively, a wind-deflecting fairing of the present embodimentcould be designed to be more extensive in forward extent, while beingsomewhat limited in extending to no lower than the level of the axle,while still yielding a reduction in overall vehicle drag, especiallywhile the vehicle is operating under a variety of relative externalheadwind conditions. Thus, a variety of configurations for extending thesurfaces of the wind-deflecting fairing of the present embodiment isincluded that will yield an effective reduction in overall vehicle drag.

In consideration of further embodiments described below, the operatingprinciples described above will generally apply, and may be referredthereto.

Second Embodiment—FIGS. 1 and 3

As shown in FIGS. 1 and 3, an embodiment comprises an inclinedaerodynamic deflector panel assembly 15 attached to and mountedunderneath the body of a trailer 16 for a commercial vehicle. Theinclined deflector panel assembly 15 is located forward of the rearwheel assembly 17 and located in front of trailing wheel sets 18 whichwould otherwise be exposed to headwinds when the vehicle is in forwardmotion. The inclined deflector panel assembly 15 is planar in shape,mounted inclined in a forwardly-angled orientation with the upper edgemore forwardly located and the lower surface located more rearward onthe vehicle. The inclined deflector panel assembly 15 spans the lateralwidth of the trailer 17, and where aligned directly in front of thewheel sets 18 ideally extends downward to no lower than the level of theaxle. The inclined deflector panel assembly 15 is located proximal tothe trailing wheel assembly 18 in order to deflect headwinds onto theexposed lower wheel surfaces, and to deflect headwinds from directlyimpinging on the central axle assembly 19, thereby reducing overallvehicle drag and improving propulsive efficiency.

Third Embodiment—FIGS. 4 and 5

As shown in FIGS. 4 and 5, an embodiment comprises a channeledaerodynamic wheel deflector panel assembly 25 attached to and mountedunderneath the body of a trailer 16 for a commercial vehicle. Thechanneled wheel deflector panel assembly 25 is located forward of therear wheel assembly 17 and located directly in front of a trailing wheelset 18 which would otherwise be exposed to headwinds when the vehicle isin forward motion. The channeled wheel deflector panel assembly 25includes a deflector plate 22 which is generally planar in shape,mounted inclined in a forwardly-angled orientation with the upper edgemore forwardly-located and the lower surface located more rearward onthe vehicle. The channeled wheel deflector panel assembly 25 includesforwardly-projecting end plates 24 attached to either side edge of thedeflector plate 22, forming a channeled deflector panel assembly 25 tofunnel headwinds directly onto the lower wheel surfaces, minimizing anyoutwardly deflected headwind from otherwise impinging on the trailingupper wheel surfaces.

The channeled wheel deflector panel assembly 25 ideally extends downwardto no lower than the level of the axle 19 and is located proximal to thetrailing wheel set 18 in order to deflect and funnel headwinds onto theexposed lower wheel surfaces, thereby reducing overall vehicle drag andimproving propulsive efficiency.

Fourth Embodiment—FIGS. 4 and 6

As shown in FIGS. 4 and 6, an embodiment comprises a channeledaerodynamic deflector panel assembly 30 attached to and mountedunderneath the body of a trailer 16 for a commercial vehicle. Thechanneled deflector panel assembly 30 is located forward of the rearwheel assembly 17 and located in front of both trailing wheel sets 18which would otherwise be exposed to headwinds when the vehicle is inforward motion. The channeled deflector panel assembly 30 includes adeflector plate 28 which is generally planar in shape, mounted inclinedin a forwardly-angled orientation with the upper edge moreforwardly-located and the lower surface located more rearward on thevehicle. The deflector plate 28 spans the lateral width of the trailer16, and where directly aligned in front of the wheels ideally extendsdownward to no lower than the level of the axle 19. The channeleddeflector panel assembly 30 includes forwardly-projecting end plates 32attached to either side edge of the deflector plate 28, forming achanneled deflector panel assembly 30 to funnel headwinds directly ontothe lower wheel surfaces and minimize any outwardly deflected headwindfrom otherwise impinging on the trailing upper wheel surfaces. Althoughnot shown, between the wheel sets 18, the deflector plate 28 may extendfurther downward to deflect headwinds well below the central axleassembly 19.

The channeled deflector panel assembly 30 is located proximal to thetrailing wheel set 18 in order to deflect headwinds onto the exposedlower wheel surfaces, and to deflect headwinds from directly impingingon the central axle assembly 19, thereby reducing overall vehicle dragand improving propulsive efficiency.

Fifth Embodiment—FIGS. 7 and 5

As shown in FIG. 7 in side view, and as shown in FIG. 5 when viewed incross-section from the front of the vehicle, an embodiment comprises thechanneled aerodynamic wheel deflector panel assembly 25 identical tothat of the third embodiment above, together with removable upper wheelskirt panels 38 covering the outside of the trailing wheel sets 18. Theupper wheel skirt panels 38 also ideally extend downward to no lowerthan the level of the axle 19.

The upper wheel skirt panels 38 extend from the deflector plate 22rearward to cover adjacent trailing wheel sets 18, thereby shielding thetrailing upper wheels from external headwinds. The channeled wheeldeflector panel assembly 25 used in combination with the upper wheelskirt panels 38 reduces overall vehicle drag and improves propulsiveefficiency.

Sixth Embodiment—FIGS. 7 and 6

As shown in FIG. 7 in side view, and as shown in FIG. 6 when viewed incross-section from the front of the vehicle, an embodiment comprises thechanneled aerodynamic deflector panel assembly 30 identical to that ofthe fourth embodiment above, together with removable upper wheel skirtpanels 38 covering the outside of the trailing wheel sets 18. The upperwheel skirt panels 38 also ideally extend downward to no lower than thelevel of the axle 19.

The upper wheel skirt panels 38 extend from the deflector plate 28rearward to cover adjacent trailing wheel sets 18, thereby shielding thetrailing upper wheels from external headwinds. The channeled deflectorpanel assembly 30 used in combination with the upper wheel skirt panels38 reduces overall vehicle drag and improves propulsive efficiency.

Seventh Embodiment—FIGS. 8 and 2

As shown in FIG. 8 in side view, and as shown in FIG. 2 when viewed incross-section from the front of the vehicle, an embodiment comprises anaerodynamic wheel deflector panel 45 is attached to and mountedunderneath the body of a trailer 16 for a commercial vehicle. The wheeldeflector panel 45 is located forward of the rear wheel assembly 17 andlocated in front of a trailing wheel set 18, which would otherwise beexposed to headwinds when the vehicle is in forward motion. The wheeldeflector panel 45 is planar in shape, sufficiently wide to deflectheadwinds from directly impinging on the upper wheels of the trailingwheel set, mounted vertically and shown oriented parallel to the axle19. The wheel deflector panel 45 ideally extends downward no lower thanthe level of the axle 19, and is located proximal to the trailing wheelset 18 in order to deflect headwinds substantially toward either theoutside or the inside of the wheel set 18, or onto the lower wheelsurfaces—thereby reducing overall vehicle drag and improving propulsiveefficiency.

This simple wheel deflector panel configuration is appropriate for usewhen limited clearance space exists in front of the trailing wheel set.

Eighth Embodiment—FIGS. 8 and 3

As shown in FIG. 8 in side view, and as shown in FIG. 3 when viewed incross-section from the front of the vehicle, an embodiment comprises anaerodynamic deflector panel 50 is attached to and mounted underneath thebody of a trailer 16 for a commercial vehicle. The deflector panel 50 islocated forward of the rear wheel assembly 17 and located in front of atrailing wheel sets 18 which would otherwise be exposed to headwindswhen the vehicle is in forward motion. The deflector panel 50 is planarin shape, spans the lateral width of the trailer 16, and where aligneddirectly in front of the wheel sets 18 ideally extends downward to nolower than the level of the axle 19. The deflector panel 50 is mountedvertically and parallel to the axle 19. The deflector panel 50 islocated proximal to the trailing wheel sets 18 in order to deflectheadwinds substantially toward either the outside of the trailing upperwheels, under the central axle assembly, or onto the lower wheelsurfaces—thereby reducing overall vehicle drag and improving propulsiveefficiency.

This simple deflector panel configuration is appropriate for use whenlimited clearance space exists in front of the trailing wheel assembly.

Ninth Embodiment—FIGS. 9 and 2

As shown in FIG. 9 in side view, and similar to as shown in FIG. 2 whenviewed in cross-section from the front of the vehicle, an embodimentcomprises the aerodynamic wheel deflector panel 45 identical to that ofthe seventh embodiment above, together with removable upper wheel skirtpanels 42 covering the outside of the trailing wheel sets 18. The upperwheel skirt panels 42 also ideally extend downward to no lower than thelevel of the axle 19.

The upper wheel skirt panels 42 extend from the deflector panel 45rearward to cover adjacent trailing wheel sets 18, thereby shielding thetrailing upper wheels from external headwinds. The wheel deflector panel45 used in combination with the upper wheel skirt panels 42 reducesoverall vehicle drag and improves propulsive efficiency.

This simple wheel deflector panel configuration is appropriate for usewhen limited clearance space exists in front of the wheel sets and wherethe use of exterior wheel skirts panels is permitted.

Tenth Embodiment—FIGS. 9 and 3

As shown in FIG. 9 in side view, and similar to as shown in FIG. 3 whenviewed in cross-section from the front of the vehicle, an embodimentcomprises the aerodynamic wheel deflector panel 50 identical to that ofthe eighth embodiment above, together with removable upper wheel skirtpanels 42 as used in the ninth embodiment above. The deflector panel 50used in combination with the upper wheel skirt panels 42 reduces overallvehicle drag and improves propulsive efficiency.

This simple wheel deflector panel configuration is appropriate for usewhen limited clearance space exists in front of the wheel sets, wheredeflecting headwinds from directly impinging on the central axleassembly 19 is needed, and where the use of exterior wheel skirts panelsis permitted.

Eleventh Embodiment—FIGS. 10 and 11

As shown in FIGS. 10 and 11, an embodiment comprises an aerodynamicvehicle skirt assembly 60 is attached to and mounted underneath the bodyof a trailer 16 for a commercial vehicle. The vehicle skirt assembly 60is located forward of the rear wheel assembly 17 which would otherwisebe exposed to headwinds when the vehicle is in forward motion. Thevehicle skirt assembly 60 ideally extends downward to no lower than thelevel of the axle 19 of the trailing wheel set 18, leaving lower wheelsurfaces of the trailing wheel set 18 exposed to headwinds.

The vehicle skirt assembly 60 is shown mounted to the trailer 16 withthe forwardmost end of the vehicle skirt assembly 60 inset toward thecenterline of the trailer 16 to a position in general longitudinalalignment with the inside of—and thereby substantially in front of—theinnermost surface of the trailing wheel set 18. Extending rearward, thevehicle skirt assembly 60 progressively varies in position toward theoutside of the body of the trailer 16, extending more rapidly toward theoutside wheel when nearest the rear end, which is located proximate tothe trailing wheel set 18. The rear end of the vehicle skirt assembly 60is located near the outer side of the wheel set 18, thereby deflectingheadwinds substantially toward the outside of the upper wheel surfacesand below onto the lower wheel surfaces.

The vehicle skirt assembly 60 may be constructed from either a singlepanel or from multiple panels arranged end-to-end. The vehicle skirtassembly 60 may be constructed with resilient materials, especiallyalong the lower edge that may occasionally contact road obstacles. Thevehicle skirt assembly 60 may also be mounted to the trailer 16 bydeflectable resilient means, returning the vehicle skirt assembly 60 tothe proper aerodynamic position after contacting road obstacles.

Twelfth Embodiment—FIG. 12

As shown in FIG. 12, an embodiment comprises the aerodynamic vehicleskirt assembly 60 identical to that of the eleventh embodiment above,together with removable upper wheel skirt panels 42 covering the outsideof the trailing wheel sets 18 as used in the tenth embodiment above.

The upper wheel skirt panels 42 extend from the aerodynamic vehicleskirt assembly 60 rearward to cover adjacent trailing wheel sets 18,thereby ideally shielding the trailing upper wheel surfaces fromexternal headwinds. The aerodynamic vehicle skirt assembly 60 used incombination with the upper wheel skirt panels 42 reduces overall vehicledrag and improves propulsive efficiency.

Thirteenth Embodiment—FIG. 20

As shown in FIG. 20, an embodiment comprises an aerodynamic wheel skirtpanel 72 disposed adjacent to an upper sidewall of a tire of a rearwardwheel assembly 74 of a semi truck tractor 70. The skirt panel 72 isattached to the vehicle frame 76 and arranged to shield the upper tiresidewall from being otherwise exposed to headwinds, thereby reducingoverall vehicle drag and improving vehicle propulsive efficiency. Whilethe tractor is shown with dual wheel assemblies 74, the skirt panelcould also be utilized on a tractor having only a single rearward wheelassembly.

ADVANTAGES

From the description above, a number of advantages of some embodimentsbecome evident:

-   (a) An improved aerodynamic wheel set deflector panel located in    front of trailing wheels and ideally extending downward to no lower    than the axle to thereby deflect headwinds onto mechanically    disadvantaged lower wheel surfaces and to shield trailing    mechanically-advantaged upper wheel surfaces from headwinds, thereby    reduces overall vehicle drag improving propulsive efficiency.-   (b) An improved aerodynamic wheel assembly deflector panel which may    deflect headwinds below the central axle assembly, and where in    front of trailing wheels ideally extending downward to no lower than    the axle to thereby deflect headwinds onto mechanically    disadvantaged lower wheel surfaces and to shield trailing    mechanically-advantaged upper wheel surfaces from headwinds, thereby    reduces overall vehicle drag improving propulsive efficiency.-   (c) An improved aerodynamic deflector and skirt assembly where in    front of trailing wheels ideally extending downward to no lower than    the axle to thereby deflect headwinds onto mechanically    disadvantaged lower wheel surfaces and to shield trailing    mechanically-advantaged upper wheel surfaces from headwinds, thereby    reduces overall vehicle drag improving propulsive efficiency.-   (d) An improved aerodynamic vehicle skirt panel assembly ideally    extending downward to no lower than the axle to thereby deflect    headwinds onto mechanically disadvantaged lower wheel surfaces and    to shield trailing mechanically-advantaged upper wheel surfaces from    headwinds, reduces total weight of the skirt assembly, improves the    skirt ground clearance of road obstacles, and reduces overall    vehicle drag improving propulsive efficiency.-   (e) An improved aerodynamic wheel skirt panel assembly ideally    extending downward to no lower than the axle to thereby deflect    headwinds onto mechanically disadvantaged lower wheel surfaces and    to shield trailing mechanically-advantaged upper wheel surfaces from    headwinds reduces overall vehicle drag thereby improving propulsive    efficiency.

CONCLUSIONS, RAMIFICATIONS, AND SCOPE

Exposed wheels can generate considerable drag forces on a movingvehicle. These forces are directed principally near the top of thewheel, rather than being more evenly distributed across the entireprofile of the wheel. Furthermore, these upper-wheel drag forces arelevered against the axle, thereby magnifying the counterforce requiredto propel the vehicle. As a result, a reduction in drag upon the upperwheel generally enhances propulsive efficiency significantly more than acorresponding drag reduction on other parts of the vehicle.

With the net drag forces being offset and directed near the top of thewheel, nearly equivalent countervailing reaction forces—also opposingvehicle motion—are necessarily transmitted to the wheel at the ground.These reaction forces necessitate augmented down-forces to be applied inhigher speed vehicles, in order to maintain static frictional groundcontact and, thereby, vehicle traction and directional stability. Aswings and other means typically used to augment these down-forces insuch vehicles can add significant drag, it becomes evident thatsubstantial effort should be made to reduce the upper wheel drag forceson most high-speed vehicles.

Moreover, since the lower wheel drag forces suffer a mechanicaldisadvantage over propulsive counterforces, using shielding devices todeflect headwinds from impinging on lower wheel surfaces can increaseoverall vehicle drag. Given these considerations, it becomes evidentthat drag-reducing vehicle deflectors and skirts should be ideallylimited to lengths that inhibit vehicle headwinds from directlyimpinging on only the upper wheel surfaces, leaving the lower wheelsurfaces exposed.

While the embodiments shown illustrate application generally to thetrailers of industrial trucks, the embodiments could be similarlyapplied other trucks and vehicle types having wheel assemblies exposedto headwinds. And while the embodiments shown include skirt assembliesformed from relatively inexpensive flat panels, somewhat curved panelscould also be used. Further examples of alternative embodiments includehaving deflector panels mounted at various angles, all ideally limitedin height to extend downward to no lower than the level of the axle.

Although not shown, in the case where additional space exists in frontof the wheel assembly, the wheel deflector panel of the ninth embodimentcould instead be mounted in nonparallel to the axle in order to deflectwinds not only downward, but also to either side of the trailing wheelassembly.

And although not shown, the wheel skirt panel assembly of the thirteenthembodiment could further include a fender covering the front upper tiresurfaces and could also extend over the top of wheel assemblies as well.Furthermore, this embodiment could also be disposed on the rearwardwheel assemblies of the trailer as well.

In addition, the embodiments generally can include various methods ofresilient mounting to the vehicle body permitting the panels to deflectwhen impacted by road obstructions and return undamaged to their normalaerodynamic position.

Accordingly, the embodiments should not be limited to the specificexamples illustrated and described above, but rather to the appendedclaims and their legal equivalents.

I claim:
 1. An apparatus for reducing drag on a tractor of a semitruck,wherein said tractor has a rearward wheel assembly otherwise exposed toa headwind impinging upon an outermost upper sidewall of an outermosttire of the wheel assembly while the tractor is in forward motion, withsaid outermost upper sidewall being located wholly above a midmost levelof an axle of the wheel assembly, said apparatus comprising: anaerodynamic deflector panel assembly attached to the frame of thetractor; the deflector panel assembly comprising one or more panelsextending alongside and adjacent to the outermost upper tire sidewall; acritically aligned section of the one or more panels consisting ofportions thereof that are disposed immediately adjacent to the outermostupper tire sidewall; the critically aligned section spanning across acritical elevation positioned not lower than an intermediate elevationabove the ground equal to 75 percent of the outer diameter of the wheelassembly; and the critically aligned section extending not lower than alowermost level located at an elevation above the ground equal toone-third of the outer diameter of the wheel assembly, whereby thecritically aligned section is disposed immediately adjacent to the wheelassembly to divert a substantial portion of the headwind from otherwiseimpinging upon the a major upper drag-inducing surface of the outermostupper tire sidewall.
 2. The apparatus of claim 1, further comprising: afirst said rearward wheel assembly disposed immediately adjacent infront of a second rearward wheel assembly; and the one or more panelsextending alongside and adjacent to a laterally outermost sidewallsurface of a tire on each of said two adjacent rearward wheelassemblies.
 3. The apparatus of claim 1, further comprising: thelowermost level located distinctly above the midmost level.
 4. Theapparatus of claim 1, further comprising: the lowermost level locatednot lower than an elevation above the ground equal to two-thirds of theouter diameter of the wheel assembly.
 5. The apparatus of claim 2,further comprising: the lowermost level located distinctly above themidmost level.
 6. The apparatus of claim 2, further comprising: thelowermost level located not lower than an elevation above the groundequal to 60 percent of the outer diameter of the wheel assembly.
 7. Theapparatus of claim 2, further comprising: the lowermost level locatednot lower than an elevation above the ground equal to two-thirds of theouter diameter of the wheel assembly.
 8. An apparatus for reducing dragon a tractor of a semitruck, wherein said tractor has a rearward wheelassembly otherwise exposed to a headwind impinging upon an outermostupper sidewall of an outermost tire of the wheel assembly while thetractor is in forward motion, with said outermost upper sidewall beinglocated wholly above a midmost level of an axle of the wheel assembly,said apparatus comprising: an aerodynamic deflector panel assemblyattached directly to the frame of the tractor; the deflector panelassembly comprising one or more panels extending alongside and adjacentto the outermost upper tire sidewall; the deflector panel assemblydisposed immediately adjacent to a major upper drag-inducing surface ofthe outermost upper tire sidewall; the deflector panel assembly spanningacross a critical elevation positioned not lower than an intermediateelevation above the ground equal to 80 percent of the outer diameter ofthe wheel assembly; and the deflector panel assembly extending not lowerthan a lowermost level located at an elevation above the ground equal toone-third of the outer diameter of the wheel assembly, whereby thedeflector panel assembly is disposed immediately adjacent to the wheelassembly to divert a substantial portion of the headwind from otherwiseimpinging upon the major upper drag-inducing surface.
 9. The apparatusof claim 8, further comprising: a first said rearward wheel assemblydisposed immediately adjacent in front of a second rearward wheelassembly; and the one or more panels extending alongside and adjacent toa laterally outermost sidewall surface of a tire on each of said twoadjacent rearward wheel assemblies.
 10. The apparatus of claim 8,further comprising: the lowermost level located not lower than anelevation above the ground equal to 65 percent of the outer diameter ofthe wheel assembly.
 11. The apparatus of claim 9, further comprising:the lowermost level located distinctly above the midmost level.
 12. Theapparatus of claim 9, further comprising: the lowermost level locatednot lower than an elevation above the ground equal to 60 percent of theouter diameter of the wheel assembly.
 13. The apparatus of claim 9,further comprising: the lowermost level located not lower than anelevation above the ground equal to 70 percent of the outer diameter ofthe wheel assembly.
 14. A method for reducing aerodynamic drag upon atractor of a semitruck, wherein said tractor has a rearward wheelassembly otherwise exposed to a headwind impinging substantiallyunimpeded upon an outermost upper sidewall of an outermost tire of thewheel assembly while the tractor is in forward motion, with saidoutermost upper sidewall being located wholly above a midmost level ofan axle of the wheel assembly, said method comprising: forming anaerodynamic deflector panel assembly attached to the frame of thetractor; arranging the deflector panel assembly to comprise one or morepanels extending alongside and adjacent to the outermost upper tiresidewall; arranging a critically aligned section of said panels toconsist of portions thereof that are disposed immediately adjacent to athe outermost upper tire sidewall; arranging the critically alignedsection to span across a critical elevation centered about a major upperdrag-inducing surface of the outermost upper tire sidewall, with saidcritical elevation being positioned not lower than an intermediate levelin elevation above the ground equal to 75 percent of the outer diameterof the wheel assembly; and arranging the deflector panel assembly to belimited in drag-inducing extended disposition thereof so that so thatwhen the vehicle is operated at 65 mph under null wind conditions anyfurther increase in the extended disposition of the deflector panelassembly would further increase drag induced thereon to cause overallvehicle drag to increase above a critical amount otherwise induced whenthe deflector panel assembly is otherwise absent from the vehicle,whereby any reduction in vehicle drag from reduced drag on the wheelassembly is not less than the offsetting respective vehicle drag inducedby the deflector panel assembly.
 15. The method of claim 14, furthercomprising: wherein a first said rearward wheel assembly is disposedimmediately adjacent in front of a second rearward wheel assembly; andwherein the one or more panels extend alongside and adjacent to alaterally outermost sidewall surface of a tire on each of said twoadjacent rearward wheel assemblies.
 16. The method of claim 14, furthercomprising: wherein the lowermost level is located distinctly above themidmost level.
 17. The method of claim 14, further comprising: whereinthe lowermost level is located not lower than a minimum level inelevation above the ground equal to 60 percent of the outer diameter ofthe wheel assembly.
 18. The method of claim 15, further comprising:wherein the lowermost level is located distinctly above the midmostlevel.
 19. The method of claim 15, further comprising: wherein thelowermost level is located not lower than a minimum level in elevationabove the ground equal to 60 percent of the outer diameter of the wheelassembly.
 20. The method of claim 15, further comprising: wherein thelowermost level is located not lower than a minimum level in elevationabove the ground equal to 70 percent of the outer diameter of the wheelassembly.